The invention relates to an instrument for handling an insert shell and for inserting it into an outer shell of a two-part joint socket prosthesis according to the preamble of the first claim.
Joint prostheses in which one joint partner is constructed as a socket and the other joint partner is constructed as a spherical head which is rotatably mounted in the socket are known in particular from shoulder and hip-joint prostheses. These prostheses are, as a rule, of modular construction. This means, for example, that the joint socket has two parts and comprises an outer shell, which is inserted into the bone, and an insert shell, which is inserted into the outer shell and produces the joint surface, the sliding surface for the other joint partner. The insertion of the sliding shell into the outer shell takes place, as a rule, by means of press fit. For this purpose, it is necessary for the insert shell to be aligned very precisely with respect to the outer shell in order to avoid tilting during insertion. Apart from an imprecise association of the joint surface with respect to the spherical head, damage to the insert shell can occur in the case of a tilted insertion. In particular, insert shells made of ceramic material can break or even shatter.
If the insert shells are inserted by the surgeon by hand, the handling in the area around the operative wound is difficult because of the surgeon""s gloves being wet with body fluids and because of the lack of a clear view. For this reason, it is known to provide instruments which improve the handling of insert shells to be inserted. A handling instrument for joint components having joint surfaces is known from German Utility Model DE 297 02 093 U1, which handling instrument has a handle portion and a suction element arranged on the end thereof, which suction element comprises a sealing element contained therein which can be placed in a sealing manner against the joint surface of the joint component and, as a result of this, forms with this joint surface a closed suction chamber, and also a device which lowers the pressure of the suction chamber. This handling instrument is placed with the sealing element on the joint surface of the insert shell to be inserted, the pressure in the suction chamber is lowered and, as a result of this, the insert shell is picked up by suction. After the insertion of the insert shell, the pressure is raised again and the handling instrument is automatically detached from the inserted insert shell.
The known handling instrument, however, offers no certainty that the insert shell can be put on to the outer shell with the required accuracy and that, as a result of this, tilting can be avoided. Apart from this, the known handling devices are long (up to 40 cm). They are therefore unwieldy and are thus lacking in the required sensitivity during the insertion process.
The underlying object of the present invention is to introduce an instrument for handling an insert shell and for inserting it into an outer shell of a two-part joint socket prosthesis, with which instrument a simple positioning and a tilt-free insertion are possible.
The object is achieved with the aid of the characterizing features of the first claim. Advantageous developments of the invention are claimed in the subclaims.
The instrument in accordance with the invention for handling an insert shell and for inserting it into an outer shell of a two-part joint socket prosthesis comprises a handle with a holding tool connected thereto. The holding tool for the insert shell can be handled easily by means of the handle. The holding tool has at least two gripping dogs. These extend substantially radially with respect to the longitudinal axis of the handle. The claws of the gripping dogs rest on the end-face circumferential surface of the insert shell to be inserted.
As a result of the arrangement of the gripping dogs and their claws, the insert shell is held such that it is aligned precisely concentrically with respect to the longitudinal axis of the handle and at right angles to this axis. As a result of this, a precise alignment of the insert shell during insertion is possible for the surgeon. Apart from this, the short structure of the instrument gives the surgeon the required sensitivity during the insertion process.
The claws of the gripping dogs grip around the tapering outer surface of the insert shell by the same length in each case, and to the extent that, on the one hand, reliable holding but also, on the other hand, easy ejection from the claws are possible. The ejection of the insert shell from the gripping dogs of the holding tool takes place by means of a plunger, which is mounted in a sliding manner in a bore which extends concentrically with respect to the longitudinal axis of the handle. When the plunger is slid in the direction of the insert shell, the latter is pushed out of the claws of the gripping dogs and can be pressed into the outer shell of the joint socket prosthesis.
In a development of the invention, the claws of the gripping dogs have end faces which extend at right angles to the longitudinal axis. These end faces are used for placing on the end face of the outer shell. Because the claws on the gripping dogs are all the same length, when all of the dogs are placed on to the end face of the outer shell, the insert shell is positioned precisely for its insertion. This development of the gripping dogs with which, in the difficult surroundings of the operative wound, the surgeon can position the insert shell reliably and precisely for the insertion, is an advantageous aid for the surgeon.
In order that no impairment of the position of the insert shell takes place during the positioning of the instrument with the insert shell on the outer shell, the length of the claws is at least dimensioned in such a way that when they are placed on to the end face of the outer shell, the insert shell held by them still has no clamping contact with the outer shell. In this way, a correction of the positioning is possible at any time. This is ended when all of the dogs rest with their end faces on the end face of the outer shell.
In a further development of the invention, the dogs are made of an elastic material in order that the insert shell which is held can easily be pushed out of the holding tool. A further advantage consists in that insert shells which differ from each other only slightly in terms of their diameters can be held by one and the same holding tool.
In another development of the invention, the claws of the gripping dogs are produced from an elastic material. Particularly in the case of instruments which are used only once, the claws can be constructed in such a way that they even deform permanently when the insert shell is pushed out of the gripping dogs.
In a further advantageous development of the invention, the handle has a recessed grip. This recessed grip renders possible, for example, the clamping of the handle between two parallel fingers, for example the middle finger and the ring finger or the index finger and the middle finger. The recessed grip can be U-shaped, for example, and extend around the entire handle, so that optimal holding of the instrument in the hand of the surgeon is possible in any possible alignment. The pushing-out of the insert shell can then, for example, take place by means of the thumb or the upper hand.
In order that the plunger does not exert a point-focussed load on the insert shell during the ejection of the insert shell from the gripping dogs, it is advantageous if the end thereof has at least one plate with which it is supported in a ring-shaped manner on the insert shell. Such a plate has the advantage that the plunger can be used for insert shells with different joint-surface diameters.
In another development of the invention, the plunger has, on its end, a stamping head which is matched to the joint surface of the insert shell. The stamping head then has the shape of a spherical segment, the radius of which corresponds to the radius of the joint surface. Such a plunger can admittedly be used only for one diameter of an insert shell, but has the advantage that it distributes the force to be applied during insertion over a large surface and evenly on to the insert shell.
As a rule, the pressing of the insert shell into the outer shell is carried out manually by the surgeon. However, for the final fixing, a subsequent blow with a striking tool may be required. In such a case, the instrument in accordance with the invention also offers a possibility of applying such a fixing blow in a targeted manner on to the insert shell. As a result of the precise alignment of the instrument with respect to the outer shell and thus of the insert shell with respect to the outer shell, the forces applied by the blow are introduced into the insert shell evenly and precisely in accordance with their purpose.